Photosensitive compositions are well known and are useful as photoresists in the formation of printed circuit materials, in the formation of lithographic printing plates, and in proofing applications. In such systems, actinic radiation impinges on a material containing photoactive components to induce a physical or chemical change in that material. The latent image thereby produced can then be processed to form a patterned mask or an image. The photosensitive systems can be positive-working or negative-working. In positive-working systems, the areas exposed to actinic radiation are removed in the post-exposure processing step; in negative-working systems, the areas not exposed to actinic radiation are removed. Particularly useful compositions are negative-working photopolymerizable and/or photocrosslinkable compositions, hereinafter referred to collectively as "photopolymerizable." In such systems, exposure to actinic radiation initiates polymerization and/or crosslinking reactions, resulting in insolubilization of the material in suitable developer solvents. The latent image is developed by treating with the developer solvent. The photopolymerizable compositions generally contain a binder, a monomeric or oligomeric material capable of polymerizing and/or cross-linking, and a photoinitiator.
In recent years there has been increased emphasis on aqueous-developable, or aqueous-processable, compositions. Such compositions have significant advantages in terms of lower costs and environmental safeguards. Aqueous-developable systems frequently use binders having acid groups which are removable in aqueous alkaline solution. In continuous processes for the production of printed circuit materials, lithographic printing plates and proofing materials, the developer solution is recycled and used repeatedly in the development step. A problem has been the accumulation of residues, known collectively as "sludge," in the recycled developer. This sludge reduces the amount of time the developer can be used without clean up and thus reduces efficiency. Furthermore, the sludge can be intractable and difficult to remove.
Frequently, after the photoresist has served its purpose, it is removed from the substrate in what is known as a stripping step. There can also be an accumulation of sludge in the stripping solution.
It would be desirable to have a process for processing aqueous-processable photopolymerizable compositions which results in lower sludge accumulation.